The present invention concerns printing. Its operating principles have particular, although not exclusive, applicability to portable color printers.
The printing art, which began in 1300 A.D., is quite mature. Vast amounts of research and expense have been dedicated to optimizing the quality and minimizing the cost of printing machines, particularly those intended for the consumer market. Given the difficulty of meeting the demands of the human eye, the results of these efforts have been largely satisfactory. Still, the techniques employed to achieve good enough results have tended to be complicated and expensive.
Printing devices early employed for office use to meet small-computer output needs employed hammers and print-stylus matrices. These were noisy and slow and produced low-quality output. Quality improved with the use of thermal printers, but these required special paper and tended to be slow, too. A greater quality advance accompanied the advent of xerographic or special-paper laser printers, but their mechanisms are complicated, and they remain relatively expensive despite the high volumes in which they have been produced. And none of these technologies lends itself well to low-cost-per-page, high-quality color imaging.
Ink-jet and ink-bubble technologies have addressed these shortcomings to a significant extent. Ink-jet printers squirt charged ink at the paper, deflecting the ink droplets electrostatically to direct it to the desired impact location. This approach is simple in comparison with say, laser printers, and it lends itself to color printing, since successive jets of different-colored ink can be applied to the same locations. Ink-bubble-jet approaches are similarly direct: they employ explosive energy to propel ink drops to the paper from an array of sources. But the ballistic nature of the ink delivery to the paper or other print substrate in both of these approaches tends to make the image quality quite dependent on the type of paper or other image medium.